[Stoves] Cooking bands - Testing with wood - 42% more efficient than three stone

Fri Oct 21 17:40:32 CDT 2022

Dear Kevin

I have had a look at all the videos and this looks promising.

I admit I cringe when I see obvious improvements that can be made with little effort so I will jump in with more advice.

The bands could be made in a way so they do not sit on the ground, or three bricks could protrude inwards so the ring sits on them. The idea is to get air under the ring towards the end of the fire.  This would increase the firepower whereas now it drops quite a lot as the fire goes inside the upper part of the ring.

A problem might be created with this change is remnant glowing char on the bottom when the replacement fuel charge is pushed in.  I would have on hand a flat sheet to use as a scoop to wipe the coals out of that burn space.

On top there is obviously too much cold air getting into the flames which it is worth changing.  Instead of stacking bricks for a demo, can you make a brick+mud structure that encloses the fire same for an entrance hole (liberally bigger than the ring and fuel height)?  Above the ring where you push, the bricks can be made into a cylinder (polygon) so that the part of the stove now seem above the fuel and flames so there is a cylinder of brick. This will shelter the flames from side winds, "through" winds, and create a chimney effect.

The chimney effect will draw more ait to the centre, clearly lacking in the current version.

It like the ignition in the centre leading to an outward burning set of stalks. After it is all going well, the centre is air-starved. The way to feed air to the centre is have a relatively small gap above the fuel on the near wide, and perhaps two additional holes on the other two thirds. With these inlets of restricted size (compared with now) and the chimney effect, it should bring jets of air to the centre. What you are looking for as you tune the hole and gap sizes is a reduction in the height of the flames.  If there is air getting in, the flames will shorten, generally.  Long flames are an indication of inadequate air, especially in the centre.

For sure you can build such a brick stove without any mortar at all just to see how it works in principle.  If you plan the ring size and brick positions, you can create a top deck that will accept the pot bottom with something small like a triangle of rebar to create the pot-stove clearance.  I suggest 8mm bar to create the clearance.

If the bar diameter is too small, you will see smoke emerging from the fuel entrance.  If you get no smoke out the entrance, keep reducing the pot rest height until you do, then go up one step. Looking inside the flame area, if you see the flames lounging around "reeling like drunkard" instead of being drawn up stiffly, and there is no gas emerging from the front, you have the perfect balance.  Were you to measure the oxygen level in the exhaust past the pot, then calculate the excess air level, you would find it is in the range of 125% -250%.  Ideal would be 100%-125% for a simple stove. As it is, it is probably 500%-900%.  If you can get it under control, it will speed your time to boil.

Stay well
Crispin

From: Stoves <stoves-bounces at lists.bioenergylists.org> On Behalf Of K McLean
Sent: Friday, October 21, 2022 16:14
To: ajheggie at gmail.com; Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org>
Subject: Re: [Stoves] Cooking bands - Testing with wood - 42% more efficient than three stone

I don't think I shared this video<https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2F5M4ntJi_JmY&data=05%7C01%7C%7C86546ca0ee4b446ae3fd08dab3b27779%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638019876343113197%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=QFPdMZwjNaNihFd6ORpQ%2B0zrwouXCdtpi%2Ba3HwTD6rI%3D&reserved=0> with this list.  Some of the same principles are probably at play. This is a comparison of two piles of maize stalks.  The traditional way of burning maize stalks in Africa is by lighting the pile on the side, as was done with the pile on the left.  The pile on the right was lit on the top.  The difference in smoke is stunning.

On Fri, Oct 21, 2022 at 5:36 PM <ajheggie at gmail.com<mailto:ajheggie at gmail.com>> wrote:
Good stuff Kevin, this must be a similar combustion to a Swedish Candle, a short section of trunk with multuple saw cuts axially toward the bottom.

Andrew

On Fri, 21 Oct 2022 at 11:00, Kevin McLean <kevin at sun24.org<mailto:kevin at sun24.org>> wrote:
Our testing shows that cooking bands boil water with 42% less wood than a three stone cookstove with a rock bed.  Remember that rock beds make three stone cookstoves a third more efficient and reduce smoke by more than half.  Here is that article<https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.sciencedirect.com%2Fscience%2Farticle%2Fpii%2FS0973082620302775&data=05%7C01%7C%7C86546ca0ee4b446ae3fd08dab3b27779%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638019876343113197%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=OG1Th8MyiU4IUGZWv%2FDCfokhcsBMTkXgTOoeMRnmNko%3D&reserved=0>.

THREE STONE W ROCK BED

5 litres of water

Time at which water boiled: 23 minutes.

Fuel used: 1.2kg.

[https://lh3.googleusercontent.com/_euPbO3r0c5l3KczRAbIKflOnO5dIQ2J3s7yldeS8TOfgQszTdpnZYowgJ6NRSuAmR9b3_TPBg3RrK5GH8Qjf2mXq_oZJYy8pGHcb7Q-McDdA7RbtJTLUjkLti1KnSh1L0i3q0Zz7rJkgGChFA0mEXzKSDt0I8518haxVIay7oD1iVg5JtqptU3iNg]

BAND

5 litres of water.

Time at which water boiled: 15 minutes.

Fuel used: 700g.

Much less smoky than three stone with rock bed

[https://lh6.googleusercontent.com/VksVVTzfJWB0M5KnWZ6DyJWnFuAjElHzJaPZpTknVT9_S6IiNG0qnnlqdBQf-gllKBmb9MxPxZL3nGARDpoFTTbaTRvYqe-7Or5Txm50R4cuAjIV1rl2__Dv54zN_AM4vcl1PPrFU1WO_RsKroXamkWc_O40Z3ipJZ59cNpKb_UHbYKSjSzw9HrPVA]

Cooking bands are also faster and less smoky.  They do not require tending.  Elephant grass stalks, maize stalks, bamboo and cassava stems can be used in bands.  Biochar can be made.  A pair of bands (20 cm) costs around 1 USD.  Bands with a 25 cm diameter work well in school kitchens.

I hope that others can test further.  I worry that my guys may bring bias into their testing.  And they have no training on testing.  (Thanks to Norm Baker who intends to test bands with maize stalks.)

Kevin McLean
Sun24.org
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